There are any number of applications involving the handling of pressurized fluids, particularly gases, wherein pressure within the system requires monitoring for any of a variety of reasons. The apparatus utilized to monitor the system pressure may cause operational changes in the system as the pressure varies one value to another or from one range to another.
A common example of such a system is an air compressing system. Typically, a positive displacement apparatus such as a compressor is driven by an electrical motor to compress gas. Gas exiting the compressor is directed to a reservoir, typically in the form of a tank.
In controlling such an apparatus, it is desirable to terminate operation of the electrical motor, and thus the positive displacement apparatus, when the pressure within the tank attains some predetermined level. As the pressurized gas is depleted from the tank through usage or the like, it is likewise desirable to reinitiate operation of the electrical motor. Usually, such reinitiation will come upon the sensing of a second pressure level which is less than the first which caused termination of the operation of the motor, but yet is sufficiently high so as to assure the presence of adequate compressed fluid within the tank.
To provide this measure of control, pressure responsive electrical switches have been utilized to respond to the pressure in the tank and interrupt or close an electrical circuit to the motor that drives the positive displacement apparatus. Examples of electrical switches proposed for the purpose may be found in the following, commonly assigned, U.S. Pat. Nos.: 3,875,358 issued Apr. 1, 1975 to Willcox and 4,200,775 issued Apr. 29, 1980 to Bodnar.
Not untypically, a generally planar or so-called "flat" diaphragm will be associated with a pressure port. The position of the center of the diaphragm will vary proportionally to the pressure applied to the port and such a change of position is mechanically converted into motion sufficient to open or close electrical contacts at desired pressure levels.
While such switches work extremely well for their intended purpose and are highly reliable, the use of a flat diaphragm provides some difficulty in achieving good control of the pressure levels at which switching is to occur. In particular, in order for a flat diaphragm to move from one position to another, it becomes internally stressed and the internal stresses resist such movement. Consequently, the greater the pressure applied to such a diaphragm, the greater the internal resistance generated within the diaphragm itself tending to resist movement responsive to the pressure.
Furthermore, the very nature of a flat diaphragm is such that the limits of its stroke are relatively small or else rupture would occur. As a consequence of these characteristics, much care must be taken during manufacture to assure the components associated with the diaphragm rather closely hold tolerance or else the switch will be incapable of reliably operating within the intended range.
Furthermore, flat diaphragms are frequently undesirable from the applications standpoint. In particular, in order to obtain the necessary stroke of the center of the diaphragm sufficient to reliably operate other switch components, it is necessary that the diaphragm have a sufficiently large diameter as to allow such stroke without rupture. As a practical matter, this has frequently led to switches that are larger in size than would be desired because of the size limiting factor of diaphragm diameter.
Another difficulty encountered with the use of existing pressure switches resides in the need to use plumbing components such as tubes, couplings, elbows, etc. to connect the switch to the system in which it is to be employed. In a like vein, many pressure switch constructions currently in use have a great number of individual components. Because of this, assembly time is increased and reliability can be adversely affected.
The present invention is directed to overcoming one or more of the above problems.